Biannual Mammograms Recommended after 50, Even for Women with Dense Breasts

New research shows that screening for breast cancer every two years seems just as beneficial as yearly mammograms for women ages 50 to 74, with significantly fewer false-positive findings—even for women who use hormone therapy for menopause or whose breasts are dense.

These are the new findings of a new US study involving more than 900,000 women published on March 18, 2013, in JAMA Internal Medicine. The same team of researchers from the University of California, San Francisco (UCSF; USA) and Group Health Research Institute (Seattle, WA, USA) recently reported similar results for older women ages 66 to 89.

Women in their 40s with extremely dense breasts who undergo biennial mammography, in contrast, are more likely to have advanced-stage and large tumors than women who undergo yearly mammography. However, annual mammograms also resulted in more false positives, according to the new study from the Breast Cancer Surveillance Consortium (BCSC), the largest available US screening mammography dataset. Having dense breasts means it is difficult for X-rays to pass through the breast tissue.

“Increasing age and high breast density are among the strongest risk factors for the disease,” said senior author Karla Kerlikowske, MD, a professor of medicine at UCSF and a physician at the UCSF-affiliated San Francisco VA Medical Center.

Dr. Kerlikowske and other BCSC researchers reported in 2012 that risk factors may help in individual decision-making that women make with their physicians about when to begin breast cancer screening and how often to repeat it. For instance, a family history of breast cancer raises the likelihood of developing the disease but it does not increase the chances of advanced-stage tumors or large tumors. “These individual decisions involve evaluating the balance between the benefits of screening—detecting cancer early—and the potential harms, such as false-positives among healthy women,” Dr. Kerlikowske said. “Some people who are at higher risk of disease may be more willing than those at lower risk to accept such potential harms of screening.”

False-positive findings signify that women without cancer are called back for more testing, including ultrasound screening, biopsies, and more mammograms. “For women 50-74 years-old with dense breasts who are cancer-free, we estimated that more than half will be recalled for additional mammography at least once over the course of 10 years of annual screening,” said study coauthor Rebecca A. Hubbard, PhD, an assistant investigator at Group Health Research Institute who is also at the University of Washington School of Public Health. “Screening every other year decreases this risk by about a third. The risk of false-positive results is even higher for women who begin annual screening at age 40.”

When the US Preventive Services Task Force updated its breast cancer screening guidelines in 2009, it advised women to make individual decisions with their doctor. But for average-risk women, these guidelines advised screening mammography every two years for women ages 50 to 74. The guidelines recommended that women in their 40s consider their personal values regarding the benefits and dangers and then decide when to begin regular screening. The Task Force deemed evidence on risk factors other than age to be negligible at that point.

The new study was designed to explore other risk factors for breast cancer, beyond age. Extremely dense breasts and taking combination hormone therapy (with estrogen and progestin, although not with estrogen alone) had already been shown to increase women’s rates of advanced-stage or large tumors. The new study supplements this evidence by demonstrating, regardless of hormone use or breast density, screening every other year did not raise the probability of detecting advanced-stage or large tumors, compared to yearly screening.

Approximately 12%-15% of women in their 40s, and about 3%–6% of those ages 50–74, have extremely dense breasts. How does a woman know if her breasts are dense or extremely dense? “It’s a ‘Catch- 22,’” said coauthor Diana L. Miglioretti, PhD, a senior investigator at Group Health Research Institute who is also at the University of California at Davis (USA). “The only standard way to determine your level of breast density is to get a mammogram. But unless your breasts are extremely dense and you have other strong risk factors, the data don’t necessarily support your starting screening mammograms before age 50.”

Related Links:
University of California, San Francisco
Group Health Research Institute
University of California at Davis